1. Field of the Invention
This invention relates to a cooling water circulating apparatus adapted to send out cooling water flowing there into an engine or a radiator by a water pump.
2. Description of the Related Art
The known cooling apparatuses for internal combustion engines include an apparatus disclosed in Japanese Patent Laid-Open No. 88582/1997. The techniques included in this apparatus are to reduce the limitation placed on the arrangement of various auxiliary machines driven via a crankshaft, a belt and a chain, by driving a cooling water supply pump by a cam shaft, fixing the water pump to a cylinder head so as to join a discharge port of the water pump to an inlet port of a cooling water passage on a suction side of the cylinder head, thereby forming the suction side cooling water passage as a water passage on a discharge side of the water pump, whereby, even when the resistance of the suction side cooling water passage is large, negative pressure on a suction side of the water pump increases to prevent the occurrence of cavitation therein.
However, in such a related art apparatus, the cooling water is circulated by a water pump alone which is driven by a cam shaft rotated with a rotational frequency 1/2 times as high as that of the crankshaft, so that, when the temperature of the cooling water increases higher than a predetermined level, a required flow rate of the cooling water cannot be secured unless the capacity of the water pump is increased. In order to secure a required flow rate of the cooling water, the cooling water discharge performance (head) of the pump has to be improved, and, in order to increase the pump head, the dimensions of the water pump have to be increased. This causes a driving force of the water pump to increase, so that the fuel consumption also increases.